CN104005414B - Large-size rebar cast in place concrete pile supports the constructional method of column - Google Patents

Abstract

A construction method for large-diameter reinforced concrete cast-in-situ piles supporting columns, (1) prefabrication: prefabrication of reinforcement cages according to the reinforcement requirements of the pile body; Lift into the prefabricated reinforcement cage and pour the pile core concrete; (3) Connection: at the joint between the cast-in-place pile and the first layer of concrete support, cut open the pile head of the cast-in-place pile, and extend the longitudinal reinforcement of the cast-in-place pile into the supporting reinforcement cage for 30 times the diameter of the steel bar. Then pour the supporting concrete, and connect the cast-in-place pile with the support of the first floor; (4) Waterproof: at the intersection of the cast-in-place pile column and the basement floor, cut out the protective layer, set up two expansion waterstops along the periphery of the cast-in-place pile, and The cast-in-place pile columns are poured in the basement floor, and the upper cast-in-place pile columns are removed after the basement structure is completed. The invention solves the problems of insufficient bearing capacity of the conventional steel lattice column, poor bending and torsion resistance of the cross-section, and easily damaged by mechanical collisions, resulting in instability of the supporting system.

Description

Construction Method of Large Diameter Reinforced Concrete Poured Pile Supporting Upright Column

technical field

The invention relates to a cast-in-place pile, in particular to a construction method for a large-diameter reinforced concrete cast-in-situ pile supporting a column.

Background technique

The currently known support system columns in foundation pit excavation are steel lattice columns formed by inserting prefabricated steel members into large-diameter reinforced concrete pouring piles (diameter 1000 or 1200mm). bottom elevation, lower the reinforcement cage, pour concrete to the elevation of the bottom of the foundation pit, then lift the prefabricated steel lattice and insert it into the pile core concrete for no less than 2000mm, or weld the prefabricated steel lattice and the reinforcement cage at the lower part of the cast-in-place pile and hoist them into the pile together Then pour concrete to the design elevation of the bottom of the basement floor, and backfill the upper part with sand to facilitate the stripping of the steel lattice after excavation of the foundation pit. The steel lattice structure is usually welded by 4 full-length equilateral angle steel 14#~20# (thickness 14~20mm) and 4 slabs of 520×250×12mm, the vertical spacing of the slabs is 1000mm, the section of the steel lattice column It is a square with a side length of 600~800mm. At the connection between the inner support and the steel column, pass the longitudinal reinforcement of the inner support through the gap between the two sides of the steel lattice or the gap between the two angle steels. If it cannot pass through, weld the longitudinal reinforcement of the inner support to the angle steel, and then pour Concrete forms a whole. Where the steel column passes through the basement floor, the steel lattice structure is wrapped with water-proof steel plates, and the steel lattice structure is poured into the basement floor. After the construction of the basement structure is completed, the upper steel lattice structure is cut off. Its main disadvantage is that the construction process is more complicated. The steel lattice column needs to be processed and manufactured by professional technicians in the factory. Large; second, the cost of steel lattice columns is high, especially for multi-layer (more than 3 layers) long-span support systems, which are self-heavy, high-grade steel specifications and grades, and use a large amount and are difficult to reuse, resulting in waste; the third is vertical The load-bearing capacity and cross-section bending resistance are relatively weak, and the large-span, multi-layer support system or beams are overloaded when overloaded, or the support system produces large out-of-plane deformation due to horizontal force transmission, which will easily lead to distortion and deformation of the steel lattice section. The support system is stable and safe. In addition, the steel lattice column has poor mechanical impact ability, and is easily damaged by large-scale excavation machinery during the excavation process of the foundation pit.

Contents of the invention

The technical problem to be solved by the present invention is to provide a construction method of a large-diameter reinforced concrete pouring pile supporting a column, so as to solve the problems existing in the construction and use of the steel column at present.

In order to solve the above-mentioned technical problems, the technical solution of the present invention is: a construction method of a large-diameter reinforced concrete cast-in-place pile supporting a column, comprising the following steps:

(1) Prefabrication: Prefabricate the reinforcement cage according to the reinforcement requirements of the pile body, and the pre-embedded and supported connecting steel bars need to be bound and welded on the corresponding position of the steel cage in advance;

(2) Construction: After leveling the site, measuring and determining the position of the column piles, constructing holes on the existing ground to the design elevation of the bearing layer at the bottom of the piles, then hoisting into the prefabricated steel cage, pouring pile core concrete; forming holes in the pouring piles and The verticality must be strictly controlled when the reinforcement cage is hoisted in. The verticality is required to be no more than 1%, and the pile position deviation must not be greater than 50mm;

(3) Connection: At the joint between the cast-in-place pile and the concrete support beam on the first floor, cut out the pile head of the cast-in-place pile, extend the longitudinal reinforcement of the cast-in-place pile into the supporting reinforcement cage 30 times the diameter of the steel bar, then pour the supporting concrete, and connect the cast-in-place pile to the first floor The support beams are connected together; when several layers of concrete inner support beams are set, a certain number of steel bars are pre-embedded at the intersection of the cast-in-situ piles and the inner support beams. Cut out the concrete of the protective layer of cast-in-place piles, extend the pre-embedded steel bars into the supporting steel cage and connect them with the supporting longitudinal bars. The concrete at the junction of the pile and column is chiseled, and finally the concrete for the inner support is poured, so as to connect the inner support beam with the cast-in-situ pile column;

(4) Waterproof: At the junction of the cast-in-place pile column and the basement floor, cut out the protective layer, set up and down two expansion water-stop strips along the periphery of the cast-in-place pile, and pour the cast-in-place pile column into the basement floor, and remove the upper part after the basement structure is completed. Cast-in-situ piles are used to ensure that the waterproof effect of the basement floor is not affected.

As an improvement, before the prefabricated steel cage, it is necessary to lay out the columns according to the internal support system, and check and calculate the self-weight of the internal support system, the supporting axial force and the vertical pressure and horizontal component force formed by the upper overload of a single column, and then according to the "Building Pile Foundation Technical Specifications (JGJ94-2008)" to check the vertical and horizontal bearing capacity, determine the diameter and effective embedding depth of the cast-in-place pile, and select the diameter of the cast-in-situ pile to be 600~1000mm; calculate the pile body according to the horizontal component force shared by the cast-in-situ pile column Bending moment, so as to determine the reinforcement of cast-in-place pile.

As an improvement, in step (3), the connection between the pre-embedded reinforcement and the supporting main reinforcement is welding or binding.

As an improvement, in step (3), the cast-in-place pile and the inner support beam are intersected by two-way or multi-directional support, and a reinforced concrete ring with a sagittal diameter of 600-800mm is set outside the pile to enhance the overall stiffness of the support node, and the reinforcement in the ring meets The minimum reinforcement ratio is sufficient.

As an improvement, in step (3), planting reinforcement can be used instead of pouring concrete at the junction of the inner support beam and the cast-in-situ pile column. The length of the steel cage is not less than 35 times the diameter of the steel bar, and rings can be set at the intersection of multi-directional supports.

As an improvement, if the internal support system uses steel pipe support, the prefabricated steel bracket is nailed to the cast-in-place pile with expansion bolts to support the steel pipe support.

The beneficial effect brought by the present invention compared with prior art is:

1. Large-diameter reinforced concrete cast-in-place piles are used as columns, and the steel cages are manufactured at the construction site. The construction technology of cast-in-place piles forming holes, placing steel cages and pouring concrete is mature, and the operation is simple and the quality is controllable;

2. Its vertical and horizontal bearing capacity and cross-section bending and torsion resistance are greatly improved, which effectively solves the problem of instability of the support system caused by insufficient vertical bearing capacity or distortion and deformation of the steel column under the action of strong horizontal force;

3. The anti-collision and lateral soil pressure resistance of the large-diameter cast-in-situ pile column is much higher than that of the steel lattice column welded by angle steel and patch plate, which solves the problem that the steel column is easily damaged by large machinery during the excavation of the foundation pit. The problem of collision damage;

4. Large-diameter cast-in-situ piles are used as columns, which have strong integrity and stability. At the same time, they can also be used as anti-floating piles in the basement, realizing one pile for two purposes, and saving project cost;

5. Large-diameter cast-in-situ piles are used as columns. The vertical load of the pile body is mainly borne by concrete. The bending moment of the pile body is small and the reinforcement ratio is low. Compared with steel lattice columns, the amount of steel is greatly reduced, and the cost of a single column is greatly reduced. The deeper the foundation pit, the more obvious the effect of reducing the investment cost, and the average cost saving is about 20-50%;

6. For multi-directional support nodes, set a reinforced concrete ring with a diameter of 600~800mm around the column of the cast-in-place pile, and pour each support node and column pile together to effectively improve the stiffness and stability of the support node, especially for large-span The ring-shaped support system greatly improves the ability of the support system to resist uneven deformation and enhances the safety of support.

Description of drawings

Figure 1 is a schematic diagram of cast-in-place piles.

Figure 2 is a schematic diagram of reinforcement of the cast-in-situ pile column.

Figure 3 is a schematic diagram of the connection between the cast-in-situ pile column and the first-floor concrete support beam.

Figure 4 is a schematic diagram of the connection between the cast-in-situ pile column and the concrete support beam at the pile body (1).

Figure 5 is a schematic diagram of the connection between the cast-in-situ pile column and the concrete support beam at the pile body (2).

Fig. 6 is a schematic diagram of the nodes of the reinforced concrete rings around the column of the cast-in-place pile.

Figure 7 is a schematic diagram of the connection between the cast-in-situ pile column and the steel pipe support bracket.

Figure 8 is a schematic diagram of the connection between the cast-in-situ pile column and the basement floor.

Fig. 9 is a process flow chart of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings of the description.

A construction method for a large-diameter reinforced concrete pouring pile supporting a column, as shown in Figure 9, comprising the following steps:

(1) Design and calculation: As shown in Figures 1 and 2, according to the arrangement of the vertical columns of the internal support system, the self-weight of the internal support system, the support axial force and the vertical pressure and horizontal component force formed by the upper overload to be shared by a single column are checked and calculated respectively. , and then check the vertical and horizontal bearing capacity according to the "Technical Specifications for Building Pile Foundations (JGJ94-2008)" to determine the diameter D and effective embedding depth H of the cast-in-place pile. The shared horizontal component force is used to calculate the pile body bending moment, so as to determine the pile body reinforcement of the cast-in-situ pile, such as the longitudinal reinforcement 1, the spiral reinforcement 3 and the stiffening hoop 2 of the cast-in-place pile.

(2) Prefabrication: Prefabricate the reinforcement cage according to the reinforcement requirements of the pile body, and the pre-embedded and supported connecting steel bars need to be bound and welded on the corresponding position of the steel cage in advance;

(3) Construction: After leveling the site, measuring and determining the position of the column piles, constructing holes on the existing ground to the design elevation of the bearing layer at the bottom of the pile, then hoisting the prefabricated steel cage 10, pouring pile core concrete; forming holes in the pouring piles And the verticality must be strictly controlled when the reinforcement cage 10 is hoisted in, the verticality is required to be no more than 1%, and the pile position deviation must not be greater than 50mm;

(4) Connection: As shown in Figure 3, at the joint between the cast-in-place pile 7 and the concrete support beam 4 on the first floor, the pile head of the cast-in-place pile 7 is cut open, and the longitudinal reinforcement 1 of the cast-in-place pile is inserted into the supporting reinforcement cage 10 for 30D (D is the steel bar diameter), then pour the supporting concrete, and connect the cast-in-situ pile 7 and the first-floor support beam 4 together; A certain number of steel bars are pre-embedded, and the type and quantity of the pre-embedded steel bars need to meet the cross-section shear check calculation. During the excavation, the concrete of the cast-in-place pile protection layer 5 is excavated, and the pre-embedded steel bars are inserted into the supporting steel cage 10 and connected with the supporting beam. The longitudinal reinforcement 6 is connected, the connection method between the pre-embedded reinforcement and the longitudinal reinforcement 6 of the support beam is welding or binding connection, the length of the pre-embedded reinforcement entering the support reinforcement cage 10 is not less than 30D (D is the diameter of the steel bar), and the length is 35D (D is The area of the stressed steel bar with joints within the scope of steel bar diameter) is not more than 50% of the total area; if it is a two-way or multi-directional support intersection, a reinforced concrete ring with a vector diameter of 600~800mm can be set outside the pile to enhance the overall rigidity of the support node , the reinforcement in the ring can meet the minimum reinforcement ratio; the concrete at the junction of the inner support beam 4 and the cast-in-situ pile column 71 is chiseled, and finally the concrete of the inner support beam 4 is poured, so that the inner support beam 4 and the cast-in-situ pile column 71 Connect; as shown in Figure 5, the mode of planting reinforcement 13 at the junction of inner support beam 4 and cast-in-situ pile column 71 can also be adopted instead of pouring concrete. The length entering the cast-in-place pile column 71 and the supporting reinforcement cage 10 is not less than 35D (D is the diameter of the steel bar), and a ring can be set at the intersection of multi-directional supports; as shown in Figure 6, if it is a multi-directional support, reinforced concrete can be added hoop 9;

As shown in Figure 7, if the inner support system adopts the steel pipe support 11, the prefabricated steel bracket is nailed to the cast-in-place pile 71 with the expansion bolt 12, thereby supporting the steel pipe support;

(5) Waterproof: As shown in Figure 8, at the intersection of cast-in-place pile column 71 and basement floor 15, the protective layer is dug open, and two expansion water-stop strips 14 are set up and down along the periphery of the cast-in-place pile, and the cast-in-place pile column 71 is completely poured on the In the basement floor 15, after the basement structure is completed, the upper cast-in-situ pile column 71 is removed to ensure that the waterproof effect of the basement floor 15 is not affected.

example

Panyu Shigang East Lot Development Project is located on Shigang East Road, Panyu District, Guangzhou City, with basements on the first to second floors, the building ±0.00 is equivalent to the Guangzhou urban construction elevation of 7.600m, the perimeter of the foundation pit is about 660m, and the excavation depth of the foundation pit is about 6.4 ~10.2m. Within the excavation depth of the foundation pit, the filling soil, silt, silt, plastic to hard sandy cohesive soil, etc. are sequentially exposed. Partially located in plastic to hard plastic sandy cohesive soil layer. Around the foundation pit is a 6-storey residential building close to the municipal main road and pipe pile foundation. There are sewage pipes, water supply pipes, cable trenches, etc. According to the excavation depth of the foundation pit and the geological conditions of the site, the foundation pit support of this project is mainly supported by piles. The support form is partially supported by piles and anchors, one support is used in the basement area on the first floor, two supports are used in the basement area on the second floor, and a single row of mixing piles is used on the outside to stop water. Due to the relatively deep mud layer at the bottom of the foundation pit, considering the poor stability of the steel lattice columns, in order to prevent the support system from being unstable, the supporting columns are all made of Φ1000 large-diameter reinforced concrete pouring piles as the column piles. The whole pouring is connected, and the second support is connected with the column pile by planting reinforcement on the pile body. The column piles penetrate into the strongly weathered rock not less than 8m or the medium and slightly weathered rock not less than 3m, and also serve as the uplift piles of the basement floor. At present, the project has been completed, the settlement of the column piles is small, and the maximum settlement does not exceed 5mm. After excavation, the support system is stable, and the accumulated deformation of the foundation pit is within the design allowable range, which has received good social and economic benefits.

Claims (6)

1. a construction method of a large-diameter reinforced concrete pouring pile supporting column, is characterized in that, comprises the following steps: (1) Prefabrication: Prefabricate the reinforcement cage according to the reinforcement requirements of the pile body, and bind the pre-embedded reinforcement connected by welding and support at the corresponding position on the reinforcement cage where the support is to be set; (2) Construction: Level the site, measure and determine the position of the supporting column of the cast-in-place pile, construct holes on the existing ground to the elevation of the bearing layer at the bottom of the pile, and then hoist the prefabricated steel cage into the pile core concrete; The verticality must be strictly controlled when the column is formed into a hole and the steel cage is hoisted in. The verticality is required to be no more than 1%, and the pile position deviation must not be greater than 50mm; (3) Connection: At the joint between the cast-in-place pile support column and the first-floor concrete support beam, the pile head of the cast-in-place pile support column is cut open, and the longitudinal reinforcement of the cast-in-place pile support column is extended into the support reinforcement cage by 30 times the diameter of the steel bar, and then the support concrete is poured. Connect the cast-in-place pile support columns with the first-floor support beams; when setting several layers of concrete inner support beams, a certain number of steel bars are pre-embedded at the intersection of the cast-in-place pile support columns and the inner support beams, and the type and quantity of the pre-embedded steel bars need to be To meet the cross-section shear check calculation, dig out the concrete of the protective layer of the support column of the cast-in-place pile during excavation, extend the pre-embedded steel bars into the support steel cage and connect them with the support longitudinal bars, and the length of the pre-embedded steel bars entering the support steel cage shall not be less than 30 times the diameter of the steel bar, and the concrete at the junction of the inner support beam and the cast-in-situ pile support column is chiseled, and finally the concrete of the inner support beam is poured, so as to connect the inner support beam and the cast-in-situ pile support column; (4) Waterproof: At the intersection of the cast-in-place pile support column and the basement floor, cut open the protective layer, set up and down two expansion water-stop strips along the periphery of the cast-in-place pile support column, and pour the cast-in-place pile support column into the basement floor, and the basement structure After completion, remove the upper cast-in-situ pile support column to ensure that the waterproof effect of the basement floor is not affected. 2. The construction method of large-diameter reinforced concrete cast-in-situ pile supporting column according to claim 1, characterized in that: before the prefabricated steel cage, the column needs to be arranged according to the internal support system, and the internal support system that a single column needs to share is checked and calculated respectively The vertical pressure and horizontal component force formed by self-weight, supporting axial force and upper overload, and then check the vertical and horizontal bearing capacity according to the "Technical Specifications for Building Pile Foundations (JGJ94-2008)" to determine the diameter and effective The embedding depth and the diameter of the cast-in-situ pile support column are selected from 600 to 1000mm; the pile body bending moment is calculated according to the horizontal component force shared by the cast-in-place pile support column, so as to determine the reinforcement of the cast-in-situ pile support column. 3. The construction method for supporting columns of large-diameter reinforced concrete cast-in-place piles according to claim 1, characterized in that: in step (3), the connection between the pre-embedded steel bars and the supporting main bars is welding or binding. 4. The construction method of large-diameter reinforced concrete cast-in-place pile support column according to claim 1, characterized in that: in step (3), the cast-in-place pile support column and the inner support beam are intersected by two-way or multi-directional support, and on the outside of the pile Set a reinforced concrete ring with a diameter of 600~800mm to enhance the overall stiffness of the support node, and the reinforcement in the ring should meet the minimum reinforcement ratio. 5. The construction method of large-diameter reinforced concrete cast-in-place pile support column according to claim 1, characterized in that: in step (3), at the junction of the inner support beam and the cast-in-situ pile support column, the method of planting bars can be used instead of pouring For concrete, the type and quantity of planted bars must meet the cross-section shear check calculation. The length of planted bars entering the cast-in-situ pile support columns and support reinforcement cages is not less than 35 times the diameter of the steel bars. Rings can be set at the intersection of multi-directional supports. 6. The construction method of large-diameter reinforced concrete cast-in-place pile support column according to claim 5, characterized in that: if the inner support system adopts steel pipe support, the prefabricated steel bracket is nailed to the cast-in-place pile support with expansion bolts The column is piled on the body, thereby supporting the steel pipe support.